combi boiler/radiator question.

why does 1 radiator stay warm when the heating is off?

It’s plumbed in to next door’s system. Don’t forget to thank them on their Christmas card.

why does 1 radiator stay warm when the heating is off?

Are you using hot water? Excess heat gets dumped into the radiators.

Are you using hot water? Excess heat gets dumped into the radiators.

This ^^
The boiler gets hot when you use the hot taps and needs to cool it self, so one rad is always left open (normally bathroom) to give it somewhere to dump.

Modern combi boilers shuld not need one radiator on all the time to dump excess heat. This was however common on older systems where you had a hot water tank. My guess would be its an older system converted to combi hence the rad as a heat dump being left plumbed in.

tjagain – Member
Modern combi boilers shuld not need one radiator on all the time to dump excess heat. This was however common on older systems where you had a hot water tank. My guess would be its an older system converted to combi hence the rad as a heat dump being left plumbed in.

That’s funny cos my combi system ( latest gen Ideal Vogue) is in the process of being installed and I had to chose a rad that would be without TRV so as it was open all the time, I chose the maid’s room.

cheers gents.

BA Nana – thats differnt – thats so if all the TRVs go off but the timeclock is still on you still get some circulation so the boiler does not overheat / the pump is not pumping against a closed valve

Is it not for the thermostat in the house?

Ah TJ, I was bit concerned it was being done wrong

Tiagain you had me a little concerned so I called Worcester-Bosch today. Had a long discussion about how their boilers work.
They told me categorically that my greenstar combi requires an open rad for the purposes of dumping heat from the boiler when using the hot tap (obviously and for when the trvs shut and the heating is still on.)
It is essentially the same purpose, heat demand has ended either through turning off the tap, the trvs shutting, or the heating turning off, and the boiler can then overheat, so the CH pump overuns until an internal thermostat is happy that things are cool enough.
Hence the need for an open rad in the case using the hot tap.

Warnings all over the manual for my 2 year old grant combi boiler saying i must have 1 open rad for heat dump or the warrenty is void.

The pump will run fine against a dead head no problem, centrifugal pumps will run up to their max pressure and stay there, not energy efficient but won’t hurt the pump. Displacement pumps on the other hand should never be dead headed, they have a tendancy to exploded if that happens.

That is what worcester told me. Its all about the heat dump.